1. Field of the Invention
This invention lies in the field of production techniques for silicon bodies, particularly polycrystalline large-area silicon bodies such as are useful for further processing into solar cells.
2. Prior Art
The cheapest silicon possible should be employed for the manufacture of solar cells from silicon since the demands made of these components with respect to crystal quality are not as high as in the case of semiconductor elements employable for integrated circuits. A way was therefore to be found for manufacaturing silicon crystals in a simple and inexpensive manner, i.e. without material losses insofar as possible.
A method of the type just cited is disclosed in the DE-OS No. 28 50 805. Planar silicon with a high throughput (1 m/min) can be produced for solar cells with this method in that a carrier member comprised of graphite which is provided with holes is tangentially drawn across the surface of a silicon melt in a through-feed process, whereby the carrier member is integrated in the produced silicon bodies upon crystallization of the silicon. A disadvantage of this method is that convectional currents can occur in the melt.
A further improvement with respect to the crystal quality is achieved when, as proposed in the [German] patent application No. 32 31 326.8, the molten silicon is supplied to the carrier member by means of capillaries. The capillaries discharge into a horizontal gap through which a carrier member is drawn for coating. Such carrier member consists of graphite threads and has a net-like structure. Given this drawing apparatus, the melt level in the silicon reservoir lies 10 to 15 mm lower than the horizontal gap for technical reasons. The consequence thereof is that a hydrostatic pressure .rho..multidot.g.multidot.h acts on the silicon melt which is picked up and entrained by the meshes of the carrier member, whereby h=10 through 15 mm, .rho.=the density of silicon, g=gravity, thus limiting the maximally fillable mesh size dimenstions to about 5 mm.times.5 mm.